New York — A senior nuclear regulatory official in the United States said Thursday he believed there was a “strong likelihood” of serious core damage and core melt at the Fukushima No. 1 power plant in the days immediately after the crisis began.

“There were numerous indications of high radiation levels that can only come from damaged fuel at those kinds of levels,” said Bill Borchardt, executive director for operations at the Nuclear Regulatory Commission. “So we felt pretty confident that there was significant fuel damage at the site a few days into the event.”

The NRC also had “suspicions” about the conditions of the spent fuel pools, Borchardt said after a speech at the Japan Society in New York.

Based on that assumption, he said, the NRC recommended that U.S. residents in Japan stay 80 km away from the crippled power plant, which was far beyond the Japanese government’s recommendation for residents within a 20-km radius to evacuate.